I have a small project which built with no issues when it was all in one big .rs file. I wanted to make it easier to work with, so I broke it up into modules, and the project is now structured like this:
├── GameState
│ ├── ballstate.rs
│ ├── collidable.rs
│ ├── gamestate.rs
│ ├── mod.rs
│ └── playerstate.rs
├── lib.rs
└── main.rs
In ballstate.rs
, I need to use the rand
crate. Here's an abbreviated version of the file:
extern crate rand;
pub struct BallState {
dir: Point,
frame: BoundingBox
}
impl BallState {
fn update_dir(&mut self) {
use rand::*;
let mut rng = rand::thread_rng();
self.dir.x = if rng.gen() { Direction::Forwards.as_float() } else { Direction::Backwards.as_float() };
self.dir.y = if rng.gen() { Direction::Forwards.as_float() } else { Direction::Backwards.as_float() };
}
}
However, when I run cargo build
from the top level directory, I get the following error:
GameState/ballstate.rs:42:9: 42:13 error: unresolved import
rand::*
. Maybe a missingextern crate rand
?
When I just had the extern crate declaration in my main.rs file, this worked. What's changed now that it's in a separate module?
To quote from the Crates and Modules chapter of the Rust book:
[...]
use
declarations are absolute paths, starting from your crate root.self
makes that path relative to your current place in the hierarchy instead.
The compiler is correct; there is no such thing as rand
, because you've put it inside a module, so the correct path to it would be GameState::ballstate::rand
, or self::rand
from within the GameState::ballstate
module.
You need to either move extern crate rand;
to the root module or use self::rand
within the GameState::ballstate
module.